What is the flashpoint of a substance?

The flashpoint of a substance is defined as the lowest temperature at which it can vaporize to form an ignitable mixture in air. This means that at this specific temperature, enough vapors are present to ignite if an ignition source, such as a spark or flame, is introduced. Understanding the flashpoint is crucial in fire safety, as it helps determine how a substance should be handled, stored, and transported. Knowing the flashpoint allows safety personnel to assess the risk of fire hazards in various environments and implement appropriate precautions.

The other options do not accurately reflect the concept of flashpoint. For instance, the temperature at which a substance will explode and the maximum temperature a substance can reach without igniting encompass broader phenomena associated with combustion but do not specifically relate to the formation of an ignitable vapor-air mixture. Similarly, the point at which a substance can no longer be extinguished refers to a different phenomenon pertaining to combustion dynamics, rather than the flashpoint itself. Thus, the correct definition focuses on the relationship between temperature and the ability to produce ignitable vapors.